Reducing ethyl acetate concentration in recycle streams for ethanol production processes

ABSTRACT

Recycle streams in an ethanol production process are hydrolyzed to reduce ethyl acetate concentration. In the process, acetic acid is hydrogenated to form a crude ethanol product, which undergoes a separation or purification process. Ethyl acetate is formed as a byproduct of the hydrogenation of acetic acid. The hydrolysis of recycle steams from the separation process can reduce the concentration of ethyl acetate, converting some or all of the ethyl acetate to acetic acid and ethanol.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/094,588, filed on Apr. 26, 2011, and U.S. application Ser. No.13/094,657, filed on Apr. 26, 2011, the entireties of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to processes for producingethanol and, in particular, to reducing ethyl acetate concentration inrecycle streams, preferably by hydrolysis.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from organic feedstocks, such as petroleum oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosematerials, such as corn or sugar cane. Conventional methods forproducing ethanol from organic feed stocks, as well as from cellulosematerials, include the acid-catalyzed hydration of ethylene, methanolhomologation, direct alcohol synthesis, and Fischer-Tropsch synthesis.Instability in organic feed stock prices contributes to fluctuations inthe cost of conventionally produced ethanol, making the need foralternative sources of ethanol production all the greater when feedstock prices rise. Starchy materials, as well as cellulose materials,are converted to ethanol by fermentation. However, fermentation istypically used for consumer production of ethanol, which is suitable forfuels or human consumption. In addition, fermentation of starchy orcellulose materials competes with food sources and places restraints onthe amount of ethanol that can be produced for industrial use.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. During the reduction of alkanoicacid, e.g., acetic acid, other compounds are formed with ethanol or areformed in side reactions. These impurities limit the production andrecovery of ethanol from such reaction mixtures. For example, duringhydrogenation, esters are produced that together with ethanol and/orwater form azeotropes, which are difficult to separate. In addition whenconversion is incomplete, unreacted acid remains in the crude ethanolproduct, which must be removed to recover ethanol.

EP02060553 describes a process for converting hydrocarbons to ethanolinvolving converting the hydrocarbons to ethanoic acid and hydrogenatingthe ethanoic acid to ethanol. The stream from the hydrogenation reactoris separated to obtain an ethanol product and a stream of acetic acidand ethyl acetate, which is recycled to the hydrogenation reactor.

Therefore, a need remains for improving the recovery of ethanol from acrude product obtained by reducing alkanoic acids, such as acetic acid,and/or other carbonyl group-containing compounds.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating an acetic acid and ethylacetate stream in a reactor in the presence of a catalyst to form acrude ethanol product, separating at least a portion of the crudeethanol product in a first distillation column to yield a first residuecomprising acetic acid and a first distillate comprising ethanol, ethylacetate, and water, removing water from at least a portion of the firstdistillate to yield an ethanol mixture stream comprising less than 10wt. % water, separating a portion of the ethanol mixture stream in asecond distillation column to yield a second residue comprising ethanoland a second distillate comprising ethyl acetate, and hydrolyzing atleast a portion of the second distillate to form a hydrolyzed stream.

In a second embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating an acetic acid and ethylacetate stream in a reactor in the presence of a catalyst to form acrude ethanol product, separating a portion of the crude ethanol productin a first distillation column to yield a first distillate comprisingethyl acetate and acetaldehyde, and a first residue comprising ethanol,ethyl acetate, acetic acid and water, separating a portion of the firstresidue in a second distillation column to yield a second residuecomprising acetic acid and water and a second distillate comprisingethanol and ethyl acetate, separating a portion of the second distillatein a third distillation column to yield a third residue comprisingethanol and a third distillate comprising ethyl acetate, and hydrolyzingat least a portion of the first distillate or third distillate to form ahydrolyzed stream.

In a third embodiment, the present invention is directed to a processfor producing ethanol, comprising hydrogenating an acetic acid and ethylacetate stream in a reactor in the presence of a catalyst to form acrude ethanol product, separating a portion of the crude ethanol productin a first distillation column to yield a first distillate comprisingethyl acetate, and a first residue comprising ethanol, ethyl acetate,acetic acid and water, hydrolyzing at least a portion of the firstdistillate to form a hydrolyzed stream, and recovering ethanol from thefirst residue.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, wherein like numeralsdesignate similar parts.

FIG. 1 is a schematic diagram of an ethanol production system having oneor more hydrolysis units for a two column distillation system having anintervening water removal in accordance with one embodiment of thepresent invention.

FIG. 2 is a schematic diagram of an ethanol production system having oneor more hydrolysis units for a two column distillation system inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In general, the present invention relates to processes for recoveringethanol produced by hydrogenating acetic acid in the presence of acatalyst. The hydrogenation reaction produces a crude ethanol productthat comprises ethanol, water, ethyl acetate, acetic acid, and otherimpurities. The present invention relates generally to processes inethanol production systems wherein a recycle stream is hydrolyzed toreduce the ethyl acetate concentration. The hydrolysis of ethyl acetatemay produce acetic acid and ethanol. Embodiments of the presentinvention preferably maximize ethanol yields and may also reduce wastestreams that are purged from the system.

In embodiments of the present invention, ethyl acetate that is formed asa byproduct and is recycled to a reactor that can covert both aceticacid and ethyl acetate to ethanol. Preferably, the process introducesfresh acetic acid and recycled ethyl acetate to the reactor. Dependingon the reactor conditions, there may more ethyl acetate than is desiredin the reactor due to the production of ethyl acetate from convertingacetic acid. To reduce the ethyl acetate concentrations in the reactor,the recycle streams, or a portion thereof, may be hydrolyzed. Theresulting acetic acid may be converted to ethanol and the resultingethanol may pass through the reactor. Preferably, the processes of thepresent invention operate at high conversions and an acetic acidenriched stream is not recovered and recycled to the reactor. Thus, therecycle streams to the reactor comprise ethyl acetate and may be reducedthrough hydrolysis prior to returning to the reactor.

The hydrogenation of acetic acid to form ethanol and water may berepresented by the following reaction:HOAc+2H₂→EtOH+H₂O

In theoretical embodiments where ethanol and water are the only productsof the hydrogenation reaction, the crude ethanol product comprises 71.9wt. % ethanol and 28.1 wt. % water. However, not all of the acetic acidfed to the hydrogenation reactor is typically converted to ethanol.Subsequent reactions of ethanol, such as esterification, may form otherbyproducts such as ethyl acetate. Ethyl acetate is a byproduct thatreduces the yield of ethanol of the process and increases the waste thatmust be taken out of the system.

The esterification reaction that produces ethyl acetate has liquid phaseequilibrium constant of K_(est)=4.0. (See, for example, Witzeman andAgreda in, “Acetic Acid and its Derivatives”, Marcel Dekker, NY, 1992,p. 271, the entirety of which is incorporated herein by reference.) Thehydrolysis of ethyl acetate has an equilibrium constant, K_(hyd)=0.25,which is the reciprocal of the K_(est).

${\begin{matrix}{{hydrolysis},k_{2}} \\\left. {{EtOAc} + {H_{2}O}}\leftrightarrows{{HOAc} + {EtOH}} \right. \\{{esterification},k_{1}}\end{matrix}\mspace{14mu} K_{hyd}} = {\frac{\lbrack{HOAc}\rbrack\lbrack{EtOH}\rbrack}{\lbrack{EtOAc}\rbrack\left\lbrack {H_{2}O} \right\rbrack} = 0.25}$

Excess acetic acid may be removed along with a substantial portion ofwater or a substantial portion of the ethanol and water in an initialcolumn. Until the excess acetic acid, which is not converted to productsin the hydrogenation reactor, is substantially removed from the crudeethanol product, the crude ethanol product is not at chemicalequilibrium and the composition favors esterification of ethanol withacetic acid to form ethyl acetate and water. In one embodiment of thepresent invention, substantially all of the excess acetic acid isremoved. One or more derivative streams that are formed in theseparation system may contain small amounts of acetic acid. As such, anymixture of ethanol, ethyl acetate and water in the derivative streamsare not at chemical equilibrium, and the hydrolysis of ethyl acetate isthermodynamically favored.

In one embodiment, one or more of the derivative streams obtained byrecovering and/or purifying a crude ethanol product is hydrolyzed. Inpreferred embodiments, the derivative stream to be hydrolyzed comprisesethyl acetate, ethanol, and water. Each of the components in thederivative stream may be obtained from separate streams and mixed. Inaddition, the one or more derivative streams to be hydrolyzed preferablycomprise substantially no acetic acid, e.g., less than 2 wt. % or lessthan 0.5 wt %. Although ethyl acetate may be hydrolyzed in the absenceof a catalyst, it is a preferred that a catalyst is employed to increasereaction rate. In one embodiment, the hydrolysis of the ethyl acetate isperformed under liquid phase or gas phase conditions. In one embodiment,the hydrolysis of the ethyl acetate is performed continuously underliquid phase conditions.

According to one embodiment of the invention, the derivative stream ispassed through a hydrolysis unit comprising an ion exchange resinreactor bed. The ion exchange resin reactor bed may comprise a stronglyacidic heterogeneous or homogenous catalyst, such as for example a Lewisacid, strongly acidic ion exchange catalyst, inorganic acids, andmethanesulfonic acid. Exemplary catalysts include Amberlyst™ 15 (DowChemical Company), Amberlyst™ 70, Dowex-M-31 (Dow Chemical Company),Dowex Monosphere M-31 (Dow Chemical Company), and Purolite CT typeCatalysts (Purolite International SRL). The ion exchange resin reactorbed preferably is a gel or marco-reticular bed. Ion exchange resinreactor beds may be located externally to the distillation columns orwithin a distillation column. In some embodiments, the outflow of theion exchange resin reactor bed may be directly or indirectly returned toone of the flashers and/or one of the distillation columns, e.g., theacid removal column. In one embodiment, when the system employs two ormore flashers, the outflow of the ion exchange resin reactor bed ispreferably directed to the low pressure flasher. In other embodiments, aportion of the outflow of the ion exchange resin reactor bed is fed,along with acetic acid, to the reaction zone.

In one embodiment, the crude ethanol product is fed to a distillationcolumn and ethyl acetate present in the crude ethanol product ishydrolyzed within the distillation column. The distillation column maycomprise a reactive distillation column. The distillation column maycomprise a hydrolyzing section, preferably in the upper portion of thecolumn or near the top of the column. The hydrolyzing section maycomprise an internal ion exchange resin reactor bed. In anotherembodiment, the hydrolyzing section is an enlarged portion of thecolumn, i.e., has a greater cross-sectional diameter than the lower halfof the column. This may increase the residence time of the light boilingpoint materials in the column to facilitate further hydrolysis of ethylacetate.

In further embodiments, one or more of the derivative streams may alsobe fed to the distillation column having the hydrolyzing section. Thismay allow a derivative stream containing ethyl acetate to be hydrolyzedalong with the crude ethanol product. Optionally, the derivative streammay be passed through an external ion exchange resin reactor bed beforebeing fed to the distillation column having the hydrolyzing section.

In one embodiment of the invention, other compounds may also behydrolyzed with the ethyl acetate, such as diethyl acetate (DEA).

1. Hydrogenation Process

The process of the present invention may be used with any hydrogenationprocess for producing ethanol. The materials, catalysts, reactionconditions, and separation processes that may be used in thehydrogenation of acetic acid are described further below.

The raw materials, acetic acid and hydrogen, fed to the reactor used inconnection with the process of this invention may be derived from anysuitable source including natural gas, petroleum, coal, biomass, and soforth. As examples, acetic acid may be produced via methanolcarbonylation, acetaldehyde oxidation, ethylene oxidation, oxidativefermentation, and anaerobic fermentation. Methanol carbonylationprocesses suitable for production of acetic acid are described in U.S.Pat. Nos. 7,208,624; 7,115,772; 7,005,541; 6,657,078; 6,627,770;6,143,930; 5,599,976; 5,144,068; 5,026,908; 5,001,259; and 4,994,608,the entire disclosures of which are incorporated herein by reference.Optionally, the production of ethanol may be integrated with suchmethanol carbonylation processes.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from alternate carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from more available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. Nos. 6,509,180;6,927,048; 7,074,603; 7,507,562; 7,351,559; 7,601,865; 7,682,812; and7,888,082, the entireties of which are incorporated herein by reference.See also U.S. Pub. Nos. 2008/0193989 and 2009/0281354, the entireties ofwhich are incorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. See, e.g., U.S. Pat. No. 7,884,253, the entirety ofwhich is incorporated herein by reference. Another biomass source isblack liquor, a thick, dark liquid that is a byproduct of the Kraftprocess for transforming wood into pulp, which is then dried to makepaper. Black liquor is an aqueous solution of lignin residues,hemicellulose, and inorganic chemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form synthesis gas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into synthesis gas, andU.S. Pat. No. 6,685,754, which discloses a method for the production ofa hydrogen-containing gas composition, such as a synthesis gas includinghydrogen and carbon monoxide, are incorporated herein by reference intheir entireties.

The acetic acid fed to the hydrogenation reactor may also comprise othercarboxylic acids and anhydrides, as well as aldehyde and/or ketones,such as acetaldehyde and acetone. Preferably, a suitable acetic acidfeed stream comprises one or more of the compounds selected from thegroup consisting of acetic acid, acetic anhydride, acetaldehyde, ethylacetate, and mixtures thereof. These other compounds may also behydrogenated in the processes of the present invention. In someembodiments, the presence of carboxylic acids, such as propanoic acid orits anhydride, may be beneficial in producing propanol. Water may alsobe present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the hydrogenation reactor without the need forcondensing the acetic acid and light ends or removing water, savingoverall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

The reactor, in some embodiments, may include a variety ofconfigurations using a fixed bed reactor or a fluidized bed reactor. Inmany embodiments of the present invention, an “adiabatic” reactor can beused; that is, there is little or no need for internal plumbing throughthe reaction zone to add or remove heat. In other embodiments, a radialflow reactor or reactors may be employed as the reactor, or a series ofreactors may be employed with or without heat exchange, quenching, orintroduction of additional feed material. Alternatively, a shell andtube reactor provided with a heat transfer medium may be used. In manycases, the reaction zone may be housed in a single vessel or in a seriesof vessels with heat exchangers therebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles.

The hydrogenation in the reactor may be carried out in either the liquidphase or vapor phase. Preferably, the reaction is carried out in thevapor phase under the following conditions. The reaction temperature mayrange from 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225°C. to 300° C., or from 250° C. to 300° C. The pressure may range from 10kPa to 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 1500kPa. The reactants may be fed to the reactor at a gas hourly spacevelocity (GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹,greater than 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms ofranges the GHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 12:1 to 1:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature, andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,of from 0.1 to 100 seconds, e.g., from 0.3 to 80 seconds or from 0.4 to30 seconds.

The hydrogenation of acetic acid to form ethanol is preferably conductedin the presence of a hydrogenation catalyst in the reactor. Suitablehydrogenation catalysts include catalysts comprising a first metal andoptionally one or more of a second metal, a third metal or any number ofadditional metals, optionally on a catalyst support. The first andoptional second and third metals may be selected from Group IB, IIB,IIIB, IVB, VB, VIB, VIIB, VIII transition metals, a lanthanide metal, anactinide metal or a metal selected from any of Groups IIIA, IVA, VA, andVIA. Preferred metal combinations for some exemplary catalystcompositions include platinum/tin, platinum/ruthenium, platinum/rhenium,palladium/ruthenium, palladium/rhenium, cobalt/palladium,cobalt/platinum, cobalt/chromium, cobalt/ruthenium, cobalt/tin,silver/palladium, copper/palladium, copper/zinc, nickel/palladium,gold/palladium, ruthenium/rhenium, and ruthenium/iron. Exemplarycatalysts are further described in U.S. Pat. No. 7,608,744 and U.S. Pub.No. 2010/0029995, the entireties of which are incorporated herein byreference. In another embodiment, the catalyst comprises a Co/Mo/Scatalyst of the type described in U.S. Pub. No. 2009/0069609, theentirety of which is incorporated herein by reference.

In one embodiment, the catalyst comprises a first metal selected fromthe group consisting of copper, iron, cobalt, nickel, ruthenium,rhodium, palladium, osmium, iridium, platinum, titanium, zinc, chromium,rhenium, molybdenum, and tungsten. Preferably, the first metal isselected from the group consisting of platinum, palladium, cobalt,nickel, and ruthenium. More preferably, the first metal is selected fromplatinum and palladium. In embodiments of the invention where the firstmetal comprises platinum, it is preferred that the catalyst comprisesplatinum in an amount less than 5 wt. %, e.g., less than 3 wt. % or lessthan 1 wt. %, due to the high commercial demand for platinum.

As indicated above, in some embodiments, the catalyst further comprisesa second metal, which typically would function as a promoter. Ifpresent, the second metal preferably is selected from the groupconsisting of copper, molybdenum, tin, chromium, iron, cobalt, vanadium,tungsten, palladium, platinum, lanthanum, cerium, manganese, ruthenium,rhenium, gold, and nickel. More preferably, the second metal is selectedfrom the group consisting of copper, tin, cobalt, rhenium, and nickel.More preferably, the second metal is selected from tin and rhenium.

In certain embodiments where the catalyst includes two or more metals,e.g., a first metal and a second metal, the first metal is present inthe catalyst in an amount from 0.1 to 10 wt. %, e.g., from 0.1 to 5 wt.%, or from 0.1 to 3 wt. %. The second metal preferably is present in anamount from 0.1 to 20 wt. %, e.g., from 0.1 to 10 wt. %, or from 0.1 to5 wt. %. For catalysts comprising two or more metals, the two or moremetals may be alloyed with one another or may comprise a non-alloyedmetal solution or mixture.

The preferred metal ratios may vary depending on the metals used in thecatalyst. In some exemplary embodiments, the mole ratio of the firstmetal to the second metal is from 10:1 to 1:10, e.g., from 4:1 to 1:4,from 2:1 to 1:2, from 1.5:1 to 1:1.5 or from 1.1:1 to 1:1.1.

The catalyst may also comprise a third metal selected from any of themetals listed above in connection with the first or second metal, solong as the third metal is different from the first and second metals.In preferred aspects, the third metal is selected from the groupconsisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin,and rhenium. More preferably, the third metal is selected from cobalt,palladium, and ruthenium. When present, the total weight of the thirdmetal preferably is from 0.05 to 4 wt. %, e.g., from 0.1 to 3 wt. %, orfrom 0.1 to 2 wt. %.

In addition to one or more metals, in some embodiments of the presentinvention the catalysts further comprise a support or a modifiedsupport. As used herein, the term “modified support” refers to a supportthat includes a support material and a support modifier, which adjuststhe acidity of the support material.

The total weight of the support or modified support, based on the totalweight of the catalyst, preferably is from 75 to 99.9 wt. %, e.g., from78 to 97 wt. %, or from 80 to 95 wt. %. In preferred embodiments thatutilize a modified support, the support modifier is present in an amountfrom 0.1 to 50 wt. %, e.g., from 0.2 to 25 wt. %, from 0.5 to 15 wt. %,or from 1 to 8 wt. %, based on the total weight of the catalyst. Themetals of the catalysts may be dispersed throughout the support, layeredthroughout the support, coated on the outer surface of the support(i.e., egg shell), or decorated on the surface of the support.

As will be appreciated by those of ordinary skill in the art, supportmaterials are selected such that the catalyst system is suitably active,selective and robust under the process conditions employed for theformation of ethanol.

Suitable support materials may include, for example, stable metaloxide-based supports or ceramic-based supports. Preferred supportsinclude silicaceous supports, such as silica, silica/alumina, a GroupIIA silicate such as calcium metasilicate, pyrogenic silica, high puritysilica, and mixtures thereof. Other supports may include, but are notlimited to, iron oxide, alumina, titania, zirconia, magnesium oxide,carbon, graphite, high surface area graphitized carbon, activatedcarbons, and mixtures thereof.

As indicated, the catalyst support may be modified with a supportmodifier. In some embodiments, the support modifier may be an acidicmodifier that increases the acidity of the catalyst. Suitable acidicsupport modifiers may be selected from the group consisting of: oxidesof Group IVB metals, oxides of Group VB metals, oxides of Group VIBmetals, oxides of Group VIIB metals, oxides of Group VIIIB metals,aluminum oxides, and mixtures thereof. Acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,Al₂O₃, B₂O₃, P₂O₅, and Sb₂O₃. Preferred acidic support modifiers includethose selected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅,and Al₂O₃. The acidic modifier may also include WO₃, MoO₃, Fe₂O₃, Cr₂O₃,V₂O₅, MnO₂, CuO, Co₂O₃, and Bi₂O₃.

In another embodiment, the support modifier may be a basic modifier thathas a low volatility or no volatility. Such basic modifiers, forexample, may be selected from the group consisting of: (i) alkalineearth metal oxides, (ii) alkali metal oxides, (iii) alkaline earth metalmetasilicates, (iv) alkali metal metasilicates, (v) Group IIB metaloxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metaloxides, (viii) Group IIIB metal metasilicates, and mixtures thereof. Inaddition to oxides and metasilicates, other types of modifiers includingnitrates, nitrites, acetates, and lactates may be used. Preferably, thesupport modifier is selected from the group consisting of oxides andmetasilicates of any of sodium, potassium, magnesium, calcium, scandium,yttrium, and zinc, as well as mixtures of any of the foregoing. Morepreferably, the basic support modifier is a calcium silicate, and evenmore preferably calcium metasilicate (CaSiO₃). If the basic supportmodifier comprises calcium metasilicate, it is preferred that at least aportion of the calcium metasilicate is in crystalline form.

A preferred silica support material is SS61138 High Surface Area (HSA)Silica Catalyst Carrier from Saint-Gobain N or Pro. The Saint-Gobain Nor Pro SS61138 silica exhibits the following properties: containsapproximately 95 wt. % high surface area silica; surface area of about250 m²/g; median pore diameter of about 12 nm; average pore volume ofabout 1.0 cm³/g as measured by mercury intrusion porosimetry and apacking density of about 0.352 g/cm³ (22 lb/ft³).

A preferred silica/alumina support material is KA-160 silica spheresfrom Sud Chemie having a nominal diameter of about 5 mm, a density ofabout 0.562 g/ml, an absorptivity of about 0.583 g H₂O/g support, asurface area of about 160 to 175 m²/g, and a pore volume of about 0.68ml/g.

The catalyst compositions suitable for use with the present inventionpreferably are formed through metal impregnation of the modifiedsupport, although other processes such as chemical vapor deposition mayalso be employed. Such impregnation techniques are described in U.S.Pat. Nos. 7,608,744 and 7,863,489 and U.S. Pub. No. 2010/0197485referred to above, the entireties of which are incorporated herein byreference.

In particular, the hydrogenation of acetic acid may achieve favorableconversion of acetic acid and favorable selectivity and productivity toethanol in the reactor. For purposes of the present invention, the term“conversion” refers to the amount of acetic acid in the feed that isconverted to a compound other than acetic acid. Conversion is expressedas a mole percentage based on acetic acid in the feed. The conversionmay be at least 10%, e.g., at least 20%, at least 40%, at least 50%, atleast 60%, at least 70% or at least 80%. Although catalysts that havehigh conversions are desirable, such as at least 80% or at least 90%, insome embodiments a low conversion may be acceptable at high selectivityfor ethanol. It is, of course, well understood that in many cases, it ispossible to compensate for conversion by appropriate recycle streams oruse of larger reactors, but it is more difficult to compensate for poorselectivity.

Selectivity is expressed as a mole percent based on converted aceticacid. It should be understood that each compound converted from aceticacid has an independent selectivity and that selectivity is independentfrom conversion. For example, if 60 mole % of the converted acetic acidis converted to ethanol, we refer to the ethanol selectivity as 60%.Preferably, the catalyst selectivity to ethoxylates is at least 60%,e.g., at least 70%, or at least 80%. As used herein, the term“ethoxylates” refers specifically to the compounds ethanol,acetaldehyde, and ethyl acetate. Preferably, in the reactor, theselectivity to ethanol is at least 80%, e.g., at least 85% or at least88%. Preferred embodiments of the hydrogenation process also have lowselectivity to undesirable products, such as methane, ethane, and carbondioxide. The selectivity to these undesirable products preferably isless than 4%, e.g., less than 2% or less than 1%. More preferably, theseundesirable products are present in undetectable amounts. Formation ofalkanes may be low, and ideally less than 2%, less than 1%, or less than0.5% of the acetic acid passed over the catalyst is converted toalkanes, which have little value other than as fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

Operating under the conditions of the present invention may result inethanol production on the order of at least 0.1 tons of ethanol perhour, e.g., at least 1 ton of ethanol per hour, at least 5 tons ofethanol per hour, or at least 10 tons of ethanol per hour. Larger scaleindustrial production of ethanol, depending on the scale, generallyshould be at least 1 ton of ethanol per hour, e.g., at least 15 tons ofethanol per hour or at least 30 tons of ethanol per hour. In terms ofranges, for large scale industrial production of ethanol, the process ofthe present invention may produce from 0.1 to 160 tons of ethanol perhour, e.g., from 15 to 160 tons of ethanol per hour or from 30 to 80tons of ethanol per hour. Ethanol production from fermentation, due theeconomies of scale, typically does not permit the single facilityethanol production that may be achievable by employing embodiments ofthe present invention.

In various embodiments of the present invention, the crude ethanolproduct produced by the reactor, before any subsequent processing, suchas purification and separation, will typically comprise unreacted aceticacid, ethanol and water. Exemplary compositional ranges for the crudeethanol product are provided in Table 1. The “others” identified inTable 1 may include, for example, esters, ethers, aldehydes, ketones,alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 72 15 to 72  15to 70  25 to 65  Acetic Acid 0 to 90 0 to 50 0 to 35 0 to 15 Water 5 to30 5 to 28 10 to 26  10 to 22  Ethyl Acetate 0 to 30 0 to 20 1 to 12 3to 10 Acetaldehyde 0 to 10 0 to 3  0.1 to 3   0.2 to 2   Others 0.1 to10   0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product may comprise acetic acid inan amount less than 20 wt. %, e.g., of less than 15 wt. %, less than 10wt. % or less than 5 wt. %. In terms of ranges, the acetic acidconcentration of Table 1 may range from 0.1 wt. % to 20 wt. %, e.g., 0.2wt. % to 15 wt. %, from 0.5 wt. % to 10 wt. % or from 1 wt. % to 5 wt.%. In embodiments having lower amounts of acetic acid, the conversion ofacetic acid is preferably greater than 75%, e.g., greater than 85% orgreater than 90%. In addition, the selectivity to ethanol may also bepreferably high, and is greater than 75%, e.g., greater than 85% orgreater than 90%.

2. Purification System

FIGS. 1 and 2 show a hydrogenation system 100 suitable for thehydrogenation of acetic acid and separating ethanol from the crudereaction mixture according to one embodiment of the invention. System100 comprises reaction zone 101 and distillation zone 102. Reaction zone101 comprises reactor 103, hydrogen feed line 104 and acetic acid feedline 105. In FIG. 1, distillation zone 102 comprises first column 134,water separation unit 140, and second column 138. An ion exchangereactor bed 128 is also provided. The ion exchange resin reactor bed 128preferably is a gel or marco-reticular bed. One or more of thederivative streams may be fed to the ion exchange resin reactor bed 128and the outflow of the reactor bed 128 may be directly or indirectlyreturned to the distillation zone 102 or reaction zone 101.

FIG. 1 illustrates one exemplary separation system. The reaction zone101 of FIG. 1 produces a liquid stream 112, e.g., crude ethanol product,for further separation. In one preferred embodiment, the reaction zone101 of FIG. 1 operates at above 80% acetic acid conversion, e.g., above90% conversion or above 99% conversion. Thus, the acetic acidconcentration in the liquid stream 112 may be low.

Liquid stream 112 is introduced in the middle or lower portion of afirst column 134, also referred to as acid-water column. In oneembodiment, no entrainers are added to first column 134. In FIG. 1,first column 134, water and unreacted acetic acid, along with any otherheavy components, if present, are removed from liquid stream 112 and arewithdrawn, preferably continuously, as a first residue in line 136.Preferably, a substantial portion of the water in the crude ethanolproduct that is fed to first column 134 may be removed in the firstresidue, for example, up to about 75% or to about 90% of the water fromthe crude ethanol product. First column 134 also forms a firstdistillate, which is withdrawn in line 135.

When column 134 is operated under about 170 kPa, the temperature of theresidue exiting in line 136 preferably is from 90° C. to 130° C., e.g.,from 95° C. to 120° C. or from 100° C. to 115° C. The temperature of thedistillate exiting in line 135 preferably is from 60° C. to 90° C.,e.g., from 65° C. to 85° C. or from 70° C. to 80° C. In someembodiments, the pressure of first column 134 may range from 0.1 kPa to510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375 kPa.

The first distillate in line 135 comprises water, in addition to ethanoland other organics. In terms of ranges, the concentration of water inthe first distillate in line 135 preferably is from 4 wt. % to 38 wt. %,e.g., from 7 wt. % to 32 wt. %, or from 7 to 25 wt. %. A portion offirst distillate in line 137 may be condensed and refluxed, for example,at a ratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from 1:2 to2:1. It is understood that reflux ratios may vary with the number ofstages, feed locations, column efficiency and/or feed composition.Operating with a reflux ratio of greater than 3:1 may be less preferredbecause more energy may be required to operate the first column 134. Thecondensed portion of the first distillate may also be fed to a secondcolumn 138.

The remaining portion of the first distillate in 139 is fed to a waterseparation unit 140. Water separation unit 140 may be an adsorptionunit, membrane, molecular sieves, extractive column distillation, or acombination thereof. A membrane or an array of membranes may also beemployed to separate water from the distillate. The membrane or array ofmembranes may be selected from any suitable membrane that is capable ofremoving a permeate water stream from a stream that also comprisesethanol and ethyl acetate.

In a preferred embodiment, water separator 140 is a pressure swingadsorption (PSA) unit. The PSA unit is optionally operated at atemperature from 30° C. to 160° C., e.g., from 80° C. to 140° C., and apressure of from 0.01 kPa to 550 kPa, e.g., from 1 kPa to 150 kPa. ThePSA unit may comprise two to five beds. Water separator 140 may removeat least 95% of the water from the portion of first distillate in line139, and more preferably from 99% to 99.99% of the water from the firstdistillate, in a water stream 141. All or a portion of water stream 141may be returned to column 134 in line 142, where the water preferably isultimately recovered from column 134 in the first residue in line 136.Additionally or alternatively, all or a portion of water stream 141 maybe purged via line 143. The remaining portion of first distillate exitsthe water separator 140 as ethanol mixture stream 144. Ethanol mixturestream 144 may have a low concentration of water of less than 10 wt. %,e.g., less than 6 wt. % or less than 2 wt. %. Exemplary components ofethanol mixture stream 144 and first residue in line 136 are provided inTable 2 below. It should also be understood that these streams may alsocontain other components, not listed, such as components derived fromthe feed.

TABLE 2 FIRST COLUMN 134 WITH PSA (FIG. 1) Conc. (wt. %) Conc. (wt. %)Conc. (wt. %) Ethanol Mixture Stream Ethanol 20 to 95  30 to 95 40 to 95Water <10 0.01 to 6   0.1 to 2   Acetic Acid <2 0.001 to 0.5  0.01 to0.2  Ethyl Acetate <60  1 to 55  5 to 55 Acetaldehyde <10 0.001 to 5   0.01 to 4   Acetal <0.1 <0.1  <0.05 Acetone <0.05 0.001 to 0.03   0.01to 0.025 Residue Acetic Acid <90  1 to 50  2 to 35 Water 30 to 100 45 to95 60 to 90 Ethanol <1 <0.9 <0.3

Preferably, ethanol mixture stream 144 is not returned or refluxed tofirst column 134. The condensed portion of the first distillate in line137 may be combined with ethanol mixture stream 144 to control the waterconcentration fed to the second column 138. For example, in someembodiments the first distillate may be split into equal portions, whilein other embodiments, all of the first distillate may be condensed orall of the first distillate may be processed in the water separationunit. In FIG. 1, the condensed portion in line 137 and ethanol mixturestream 144 are co-fed to second column 138. In other embodiments, thecondensed portion in line 137 and ethanol mixture stream 144 may beseparately fed to second column 138. The combined distillate and ethanolmixture has a total water concentration of greater than 0.5 wt. %, e.g.,greater than 2 wt. % or greater than 5 wt. %. In terms of ranges, thetotal water concentration of the combined distillate and ethanol mixturemay be from 0.5 to 15 wt. %, e.g., from 2 to 12 wt. %, or from 5 to 10wt. %.

The second column 138 in FIG. 1, also referred to as the “light endscolumn,” removes ethyl acetate and acetaldehyde from the firstdistillate in line 137 and/or ethanol mixture stream 144. Ethyl acetateand acetaldehyde are removed as a second distillate in line 145 andethanol is removed as the second residue in line 146. Second column 138may be a tray column or packed column. In one embodiment, second column138 is a tray column having from 5 to 70 trays, e.g., from 15 to 50trays or from 20 to 45 trays.

Second column 138 operates at a pressure ranging from 0.1 kPa to 510kPa, e.g., from 10 kPa to 450 kPa or from 50 kPa to 350 kPa. Althoughthe temperature of second column 138 may vary, when at about 20 kPa to70 kPa, the temperature of the second residue exiting in line 146preferably is from 30° C. to 75° C., e.g., from 35° C. to 70° C. or from40° C. to 65° C. The temperature of the second distillate exiting inline 145 preferably is from 20° C. to 55° C., e.g., from 25° C. to 50°C. or from 30° C. to 45° C.

The total concentration of water fed to second column 138 preferably isless than 10 wt. %, as discussed above. When first distillate in line137 and/or ethanol mixture stream comprises minor amounts of water,e.g., less than 1 wt. % or less than 0.5 wt. %, additional water may befed to the second column 138 as an extractive agent in the upper portionof the column. A sufficient amount of water is preferably added via theextractive agent such that the total concentration of water fed tosecond column 138 is from 1 to 10 wt. % water, e.g., from 2 to 6 wt. %,based on the total weight of all components fed to second column 138. Ifthe extractive agent comprises water, the water may be obtained from anexternal source or from an internal return/recycle line from one or moreof the other columns or water separators.

Suitable extractive agents may also include, for example,dimethylsulfoxide, glycerine, diethylene glycol, 1-naphthol,hydroquinone, N,N′-dimethylformamide, 1,4-butanediol; ethyleneglycol-1,5-pentanediol; propylene glycol-tetraethyleneglycol-polyethylene glycol; glycerine-propylene glycol-tetraethyleneglycol-1,4-butanediol, ethyl ether, methyl formate, cyclohexane,N,N′-dimethyl-1,3-propanediamine, N,N′-dimethylethylenediamine,diethylene triamine, hexamethylene diamine and 1,3-diaminopentane, analkylated thiopene, dodecane, tridecane, tetradecane, chlorinatedparaffins, or a combination thereof. When extractive agents are used, asuitable recovery system, such as a further distillation column, may beused to recycle the extractive agent.

Exemplary components for the second distillate and second residuecompositions for the second column 138 are provided in Table 3, below.It should be understood that the distillate and residue may also containother components, not listed in Table 3.

TABLE 3 SECOND COLUMN 138 (FIG. 1) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Second Distillate Ethyl Acetate 5 to 90 10 to 80 15 to 75Acetaldehyde <60  1 to 40  1 to 35 Ethanol <45 0.001 to 40   0.01 to35   Water <20 0.01 to 10   0.1 to 5   Second Residue Ethanol  80 to99.5 85 to 97 60 to 95 Water <20 0.001 to 15   0.01 to 10   EthylAcetate <1 0.001 to 2    0.001 to 0.5  Acetic Acid <0.5 <0.01 0.001 to0.01 

The second residue in FIG. 1 comprises one or more impurities selectedfrom the group consisting of ethyl acetate, acetic acid, acetaldehyde,and diethyl acetal. The second residue may comprise at least 100 wppm ofthese impurities, e.g., at least 250 wppm or at least 500 wppm. In someembodiments, the second residue may contain substantially no ethylacetate or acetaldehyde.

The second distillate in line 145, which comprises ethyl acetate and/oracetaldehyde, preferably is refluxed as shown in FIG. 1, for example, ata reflux ratio of from 1:30 to 30:1, e.g., from 1:10 to 10:1 or from 1:3to 3:1. In some embodiments, higher reflux ratios may be used. In oneaspect, not shown, a portion of the second distillate 145 may bedirectly returned to reactor 103. The ethyl acetate and/or acetaldehydein the second distillate may be further reacted in hydrogenation reactor103.

In one optional embodiment, water separator 140 may be after secondcolumn 138. The first distillate in line 137 may be fed to secondcolumn, and second residue in line 146 may be fed to water separator140.

In one embodiment, all or a portion of the second distillate in line 145is directed to ion exchange reactor bed 128. In another embodiment, allor a portion of the second distillate in line 145 may feed a reactivedistillation column (not shown) to hydrolyze the ethyl acetate. Thisportion of the distillate is hydrolyzed to form a hydrolyzed stream, andthe outflow stream of the ion exchange reactor bed 128 can be directlyor indirectly returned to reactor 103. Exemplary indirect return methodsmay include storing or further treating the hydrolyzed stream in one ormore additional columns to remove impurities prior to being sent toreaction zone 101. The outflow in line 131 comprises acetic acid andethanol, and preferably comprises less ethyl acetate than present inline 145. Preferably, the outflow in line 131 has at least 2% less ethylacetate than line 145, e.g., at least 10% less or at least 20% less. Interms of ranges the amount of ethyl acetate in line 131 is less thanline 145 by 2% to 25%, e.g., from 5 to 22% or from 7 to 20%. Preferably,the outflow in line 131 has at least 0.5% more ethanol than line 145,e.g., at least 2% more or at least 4% more. In terms of ranges theamount of ethanol in line 131 is more than line 145 by 0.5% to 20%,e.g., from 2 to 20% or from 4 to 20%. In addition, the outflow in line131 may also comprise less water than is present in line 145.

In one embodiment, the second distillate in line 145 and/or a refinedsecond distillate, or a portion of either or both streams, may befurther separated to produce an acetaldehyde-containing stream and anethyl acetate-containing stream. This may allow a portion of theresulting ethyl acetate-containing stream to be recycled to reactor 103(either directly or after passing through the ion exchange reactor bed128) while purging the acetaldehyde-containing stream. The purge streammay be valuable as a source of acetaldehyde.

FIG. 2 illustrates another exemplary separation system. The reactionzone 101 of FIG. 2 is similar to FIG. 1 and produces a liquid stream112, e.g., crude ethanol product, for further separation. In onepreferred embodiment, the reaction zone 101 of FIG. 2 operates at above80% acetic acid conversion, e.g., above 90% conversion or above 99%conversion. Thus, the acetic acid concentration in the liquid stream 112may be low.

In the exemplary embodiment shown in FIG. 2, liquid stream 112 isintroduced in the lower part of first column 107, e.g., lower half ormiddle third. For purposes of convenience, the columns in each exemplaryseparation process, may be referred as the first, second, third, etc.,columns, but it is understood that first column 107 in FIG. 2 operatesdifferently than the first column 134 of FIG. 1. In one embodiment, noentrainers are added to first column 107. In first column 107, a weightmajority of the ethanol, water, acetic acid, and other heavy components,if present, are removed from liquid stream 112 and are withdrawn,preferably continuously, as residue in line 114. Preferably, at least50% of the ethanol in the crude ethanol product is recovered in thefirst residue in line 114. Recovering a majority of the ethyl acetateprovides for low concentrations of ethyl acetate in the residue from theinitial column, e.g., less than 5 wt. %, less than 3 wt. % or less than1 wt. %. First column 107 also forms an overhead distillate, which iswithdrawn in line 115, and which may be condensed and refluxed, forexample, at a ratio of from 30:1 to 1:30, e.g., from 10:1 to 1:10 orfrom 1:5 to 5:1. The overhead distillate in stream 115 preferablycomprises a weight majority of the ethyl acetate from liquid stream 113.

When column 107 is operated under about 170 kPa, the temperature of theresidue exiting in line 114 preferably is from 70° C. to 155° C., e.g.,from 90° C. to 130° C. or from 100° C. to 110° C. The base of column 107may be maintained at a relatively low temperature by withdrawing aresidue stream comprising ethanol, water, and acetic acid, therebyproviding an energy efficiency advantage. The temperature of thedistillate exiting in line 115 from column 107 preferably at 170 kPa isfrom 75° C. to 100° C., e.g., from 75° C. to 83° C. or from 81° C. to84° C. In some embodiments, the pressure of first column 107 may rangefrom 0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to375 kPa. Exemplary components of the distillate and residue compositionsfor first column 107 are provided in Table 4 below. It should also beunderstood that the distillate and residue may also contain othercomponents, not listed in Table 4.

TABLE 4 FIRST COLUMN 107 (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc. (wt.%) Distillate Ethyl Acetate 35 to 95 35 to 80 35 to 60 Acetaldehyde <350.1 to 30   5 to 30 Acetal <35 0.1 to 30   5 to 30 Acetone <0.05 0.001to 0.03   0.01 to 0.025 Ethanol <50 0.1 to 15  0.5 to 10  Water  1 to 30 2 to 25  4 to 15 Acetic Acid <0.2  <0.01 not detectable Residue AceticAcid 0.1 to 50  0.5 to 40   1 to 30 Water 40 to 85 50 to 80 55 to 75Ethanol 10 to 80 15 to 60 15 to 45 Ethyl Acetate <5.0 <3.0 <1.0

In an embodiment of the present invention, column 107 may be operated ata temperature where most of the water, ethanol, and acetic acid areremoved from the residue stream and only a small amount of ethanol andwater is collected in the distillate stream due to the formation ofbinary and tertiary azeotropes. The weight ratio of water in the residuein line 114 to water in the distillate in line 115 may be greater than1:1, e.g., greater than 2:1. The weight ratio of ethanol in the residueto ethanol in the distillate may be greater than 1:1, e.g., greater than2:1.

The amount of acetic acid in the first residue may vary dependingprimarily on the conversion in reactor 103. In one embodiment, when theconversion is high, e.g., greater than 90%, the amount of acetic acid inthe first residue may be less than 10 wt. %, e.g., less than 5 wt. % orless than 2 wt. %. In other embodiments, when the conversion is lower,e.g., less than 90%, the amount of acetic acid in the first residue maybe greater than 10 wt. %.

The distillate preferably is substantially free of acetic acid, e.g.,comprising less than 1000 wppm, less than 500 wppm or less than 100 wppmacetic acid.

In one embodiment, all or a portion of the first distillate in line 115is directed to ion exchange reactor bed 128. In another embodiment, allor a portion of the first distillate in line 115 may feed a reactivedistillation column (not shown) to hydrolyze the ethyl acetate. Thisportion of the distillate is hydrolyzed to form a hydrolyzed stream, andthe outflow stream of the ion exchange reactor bed 128 can be directlyor indirectly returned to the reaction zone 101 via line 116. Exemplaryindirect return methods may include storing or further treating thehydrolyzed stream in one or more additional columns to remove impuritiesprior to being sent to reaction zone 101. The outflow in line 116comprises acetic acid and ethanol, and preferably comprises less ethylacetate than present in line 115. Preferably, the outflow in line 116has at least 2% less ethyl acetate than line 115, e.g., at least 10%less or at least 20% less. In terms of ranges the amount of ethylacetate in line 116 is less than line 115 by 2% to 25%, e.g., from 5 to22% or from 7 to 20%. Preferably, the outflow in line 116 has at least0.5% more ethanol than line 115, e.g., at least 2% more or at least 4%more. In terms of ranges the amount of ethanol in line 116 is more thanline 115 by 0.5% to 20%, e.g., from 2 to 20% or from 4 to 20%. Inaddition, the outflow in line 116 may also comprise less water than ispresent in line 115.

In some embodiments, the distillate 115 may be further separated, e.g.,in a distillation column (not shown), into an acetaldehyde stream and anethyl acetate stream. Either of these streams may be returned to thereactor 103 (either directly or through ion exchange reaction bed 128)or separated from system 100 as a separate product.

Some species, such as acetals, may decompose in first column 107 suchthat very low amounts, or even no detectable amounts, of acetals remainin the distillate or residue.

To recover ethanol, the residue in line 114 may be further separated ina second column 108, also referred to as an “acid separation column.” Anacid separation column may be used when the acetic acid concentration inthe first residue is greater than 1 wt. %, e.g., greater than 5 wt. %.The first residue in line 114 is introduced to second column 108preferably in the top part of column 108, e.g., top half or top third.Second column 108 yields a second residue in line 117 comprising aceticacid and water, and a second distillate in line 118 comprising ethanol.Second column 108 may be a tray column or packed column. In oneembodiment, second column 108 is a tray column having from 5 to 150trays, e.g., from 15 to 50 trays or from 20 to 45 trays. Although thetemperature and pressure of second column 108 may vary, when atatmospheric pressure the temperature of the second residue exiting inline 117 preferably is from 95° C. to 130° C., e.g., from 100° C. to125° C. or from 110° C. to 120° C. The temperature of the seconddistillate exiting in line 118 preferably is from 60° C. to 105° C.,e.g., from 75° C. to 100° C. or from 80° C. to 100° C. The pressure ofsecond column 108 may range from 0.1 kPa to 510 kPa, e.g., from 1 kPa to475 kPa or from 1 kPa to 375 kPa. Exemplary components for thedistillate and residue compositions for second column 108 are providedin Table 10 below. It should be understood that the distillate andresidue may also contain other components, not listed in Table 10.

TABLE 5 SECOND COLUMN 108 (FIG. 2) Conc. (wt. %) Conc. (wt. %) Conc.(wt. %) Second Distillate Ethanol  70 to 99.9 75 to 98 80 to 95 EthylAcetate <10  0.001 to 5    0.01 to 3   Acetaldehyde <5 0.001 to 1   0.005 to 0.5  Water 0.1 to 30    1 to 25  5 to 20 Second Residue AceticAcid 0.1 to 45   0.2 to 40  0.5 to 35  Water 45 to 100   55 to 99.8   65to 99.5 Ethyl Acetate <2 <1 <0.5 Ethanol <5 0.001 to 5    <2  

The weight ratio of ethanol in the second distillate in line 118 toethanol in the second residue in line 117 preferably is at least 35:1.In one embodiment, the weight ratio of water in the second residue inline 117 to water in the second distillate in line 118 is greater than2:1, e.g., greater than 4:1 or greater than 6:1. In addition, the weightratio of acetic acid in the second residue in line 117 to acetic acid inthe second distillate in line 118 preferably is greater than 10:1, e.g.,greater than 15:1 or greater than 20:1. Preferably, the seconddistillate in line 118 is substantially free of acetic acid and may onlycontain, if any, trace amounts of acetic acid. Preferably, the seconddistillate in line 118 contains substantially no ethyl acetate.

The remaining water from the second distillate in line 118 may beremoved in further embodiments of the present invention. Depending onthe water concentration, the ethanol product may be derived from thesecond distillate in line 118. Some applications, such as industrialethanol applications, may tolerate water in the ethanol product, whileother applications, such as fuel applications, may require an anhydrousethanol. The amount of water in the distillate of line 118 may be closerto the azeotropic amount of water, e.g., at least 4 wt. %, preferablyless than 20 wt. %, e.g., less than 12 wt. % or less than 7.5 wt. %.Water may be removed from the second distillate in line 118 usingseveral different separation techniques as described herein.Particularly preferred techniques include the use of distillationcolumn, membranes, adsorption units, and combinations thereof.

In some embodiments, where the second distillate comprises some ethylacetate, primarily due to the equilibrium reaction with acetic acid, afurther distillation column may be used to separate ethyl acetate andethanol as shown in FIG. 2. FIG. 2, shows a third column 125, referredto as a secondary light ends column, for removing ethyl acetate from thesecond distillate in line 118 into a third distillate in line 126.

The second distillate in line 118 is introduced to the bottom part ofthird column 125, e.g., bottom half or bottom third. Although thetemperature and pressure of third column 146 may vary, when atatmospheric pressure the temperature of the third residue exiting inline 127 preferably is from 50° C. to 120° C., e.g., from 70° C. to 115°C. or from 85° C. to 110° C. The temperature of the third distillateexiting in line 126 preferably is from 15° C. to 100° C., e.g., from 30°C. to 90° C. or from 50° C. to 80° C. In addition, the reflux ratio ofthird column 125 may be large, e.g., greater than 5:1, greater than 15:1or greater than 30:1. The pressure of third column 146 may range from0.1 kPa to 510 kPa, e.g., from 1 kPa to 475 kPa or from 1 kPa to 375kPa.

All or a portion of the third distillate 126 can be purged from thesystem or returned to the first column 107. Before returning to thefirst column 107, all or a portion of the third distillate in line 126can be hydrolyzed in ion exchange reactor bed 129. Additionally, all ora portion of the third distillate in line 126 can also be directed toion exchange reactor bed 128 (along with all or a portion of the firstdistillate 115). In another embodiment, all or a portion of the thirddistillate in line 126 (along with all or a portion of the firstdistillate 115) may feed a reactive distillation column (not shown) tohydrolyze the ethyl acetate. This portion of the third distillate(and/or the first distillate) is hydrolyzed to form a hydrolyzed stream,and the outflow stream 116 of the ion exchange reactor bed 128 can bedirectly or indirectly recycled in whole or part to reactor 103. Thethird residue in line 127 from third column 125 may comprise ethanol andoptionally water. The third residue may be further processed to recoverethanol with a desired amount of water, for example, using an ethanolproduct column. An ethanol product column, adsorption unit, membrane orcombination thereof, may be used to further remove water from thirdresidue in line 127 as necessary.

Some of the residues withdrawn from the separation zone 102 compriseacetic acid and water. Depending on the amount of water and acetic acidcontained in the residue of first column, e.g., 134 in FIG. 1, 107 inFIG. 2, the residue may be treated in one or more of the followingprocesses. The following are exemplary processes for further treatingthe residue and it should be understood that any of the following may beused regardless of acetic acid concentration. When the residue comprisesa majority of acetic acid, e.g., greater than 70 wt. %, the residue maybe recycled to the reactor without any separation of the water. In oneembodiment, the residue may be separated into an acetic acid stream anda water stream when the residue comprises a majority of acetic acid,e.g., greater than 50 wt. %. Acetic acid may also be recovered in someembodiments from the residue having a lower acetic acid concentration.The residue may be separated into the acetic acid and water streams by adistillation column or one or more membranes. If a membrane or an arrayof membranes is employed to separate the acetic acid from the water, themembrane or array of membranes may be selected from any suitable acidresistant membrane that is capable of removing a permeate water stream.The resulting acetic acid stream optionally is returned to the reactor103. The resulting water stream may be used as an extractive agent or tohydrolyze an ester-containing stream in a hydrolysis unit.

In other embodiments, for example, where the residue comprises less than50 wt. % acetic acid, possible options include one or more of: (i)returning a portion of the residue to reactor 103, (ii) neutralizing theacetic acid, (iii) reacting the acetic acid with an alcohol, or (iv)disposing of the residue in a waste water treatment facility. It alsomay be possible to separate a residue comprising less than 50 wt. %acetic acid using a weak acid recovery distillation column to which asolvent (optionally acting as an azeotroping agent) may be added.Exemplary solvents that may be suitable for this purpose include ethylacetate, propyl acetate, isopropyl acetate, butyl acetate, vinylacetate, diisopropyl ether, carbon disulfide, tetrahydrofuran,isopropanol, ethanol, and C₃-C₁₂ alkanes. When neutralizing the aceticacid, it is preferred that the residue comprises less than 10 wt. %acetic acid. Acetic acid may be neutralized with any suitable alkali oralkaline earth metal base, such as sodium hydroxide or potassiumhydroxide. When reacting acetic acid with an alcohol, it is preferredthat the residue comprises less than 50 wt. % acetic acid. The alcoholmay be any suitable alcohol, such as methanol, ethanol, propanol,butanol, or mixtures thereof. The reaction forms an ester that may beintegrated with other systems, such as carbonylation production or anester production process. Preferably, the alcohol comprises ethanol andthe resulting ester comprises ethyl acetate. Optionally, the resultingester may be fed to the hydrogenation reactor.

In some embodiments, when the residue comprises very minor amounts ofacetic acid, e.g., less than 5 wt. %, the residue may be disposed of toa waste water treatment facility without further processing. The organiccontent, e.g., acetic acid content, of the residue beneficially may besuitable to feed microorganisms used in a waste water treatmentfacility.

The columns shown in figures may comprise any distillation columncapable of performing the desired separation and/or purification. Eachcolumn preferably comprises a tray column having from 1 to 150 trays,e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75 trays.The trays may be sieve trays, fixed valve trays, movable valve trays, orany other suitable design known in the art. In other embodiments, apacked column may be used. For packed columns, structured packing orrandom packing may be employed. The trays or packing may be arranged inone continuous column or they may be arranged in two or more columnssuch that the vapor from the first section enters the second sectionwhile the liquid from the second section enters the first section, etc.

The associated condensers and liquid separation vessels that may beemployed with each of the distillation columns may be of anyconventional design and are simplified in the figures. Heat may besupplied to the base of each column or to a circulating bottom streamthrough a heat exchanger or reboiler. Other types of reboilers, such asinternal reboilers, may also be used. The heat that is provided to thereboilers may be derived from any heat generated during the process thatis integrated with the reboilers or from an external source such asanother heat generating chemical process or a boiler. Although onereactor and one flasher are shown in the figures, additional reactors,flashers, condensers, heating elements, and other components may be usedin various embodiments of the present invention. As will be recognizedby those skilled in the art, various condensers, pumps, compressors,reboilers, drums, valves, connectors, separation vessels, etc., normallyemployed in carrying out chemical processes may also be combined andemployed in the processes of the present invention.

The temperatures and pressures employed in the columns may vary. As apractical matter, pressures from 10 kPa to 3000 kPa will generally beemployed in these zones although in some embodiments subatmosphericpressures or superatmospheric pressures may be employed. Temperatureswithin the various zones will normally range between the boiling pointsof the composition removed as the distillate and the composition removedas the residue. As will be recognized by those skilled in the art, thetemperature at a given location in an operating distillation column isdependent on the composition of the material at that location and thepressure of column. In addition, feed rates may vary depending on thesize of the production process and, if described, may be genericallyreferred to in terms of feed weight ratios.

The ethanol product produced by the process of the present invention maybe an industrial grade ethanol comprising from 75 to 96 wt. % ethanol,e.g., from 80 to 96 wt. % or from 85 to 96 wt. % ethanol, based on thetotal weight of the ethanol product. Exemplary finished ethanolcompositional ranges are provided below in Table 6.

TABLE 6 FINISHED ETHANOL COMPOSITIONS Component Conc. (wt. %) Conc. (wt.%) Conc. (wt. %) Ethanol 75 to 96 80 to 96 85 to 96 Water <12 1 to 9 3to 8 Acetic Acid <1 <0.1 <0.01 Ethyl Acetate <2 <0.5 <0.05 Acetal <0.05<0.01 <0.005 Acetone <0.05 <0.01 <0.005 Isopropanol <0.5 <0.1 <0.05n-propanol <0.5 <0.1 <0.05

The finished ethanol composition of the present invention preferablycontains very low amounts, e.g., less than 0.5 wt. %, of other alcohols,such as methanol, butanol, isobutanol, isoamyl alcohol and other C₄-C₂₀alcohols. In one embodiment, the amount of isopropanol in the finishedethanol composition is from 80 to 1,000 wppm, e.g., from 95 to 1,000wppm, from 100 to 700 wppm, or from 150 to 500 wppm. In one embodiment,the finished ethanol composition is substantially free of acetaldehyde,optionally comprising less than 8 wppm acetaldehyde, e.g., less than 5wppm or less than 1 wppm.

In some embodiments, when further water separation is used, the ethanolproduct may be withdrawn as a stream from the water separation unit asdiscussed above. In such embodiments, the ethanol concentration of theethanol product may be higher than indicated in Table 6, and preferablyis greater than 97 wt. % ethanol, e.g., greater than 98 wt. % or greaterthan 99.5 wt. %. The ethanol product in this aspect preferably comprisesless than 3 wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingapplications as fuels, solvents, chemical feedstocks, pharmaceuticalproducts, cleansers, sanitizers, hydrogenation transport or consumption.In fuel applications, the finished ethanol composition may be blendedwith gasoline for motor vehicles such as automobiles, boats and smallpiston engine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, aldehydes, and higheralcohols, especially butanol. In the production of ethyl acetate, thefinished ethanol composition may be esterified with acetic acid. Inanother application, the finished ethanol composition may be dehydratedto produce ethylene. Any known dehydration catalyst can be employed todehydrate ethanol, such as those described in copending U.S. Pub. Nos.2010/0030002 and 2010/0030001, the entireties of which is incorporatedherein by reference. A zeolite catalyst, for example, may be employed asthe dehydration catalyst. Preferably, the zeolite has a pore diameter ofat least about 0.6 nm, and preferred zeolites include dehydrationcatalysts selected from the group consisting of mordenites, ZSM-5, azeolite X and a zeolite Y. Zeolite X is described, for example, in U.S.Pat. No. 2,882,244 and zeolite Y in U.S. Pat. No. 3,130,007, theentireties of which are hereby incorporated herein by reference.

In order that the invention disclosed herein may be more efficientlyunderstood, examples are provided below. The following examples describethe conversion of ethyl acetate in the recycle streams.

EXAMPLES

Simulated mixtures of ethyl acetate, water, ethanol, and small amountsof acetic acid corresponding to the recycle streams of an acetic acidhydrogenation and crude ethanol purification process of certainembodiments of the present invention are shown in Table 7 as initialcompositions (wt %). An equilibrium for the mixtures after thehydrolysis of ethyl acetate was calculated with the equilibriumcompositions (wt %) for the given initial composition shown in Table 7as well, along with the calculated ethyl acetate conversion in goingfrom the initial mixture composition to the equilibrium composition.Such conversions are calculated without the use of an ion exchange resinreactor bed, as is used in certain embodiments of the present inventionto hydrolyze ethyl acetate.

TABLE 7 RECYCLE STREAM ETHYL ACETATE HYDROLYSIS Ethyl Acetic EthylAcetate Water Ethanol Acid Acetate (wt. %) (wt. %) (wt. %) (wt. %) Conv.(%) Initial Comp. #1 60 5 35 0.001 Equilibrium Comp. #1 56.0 4.2 37.12.8 −6.7 Initial Comp. #2 56 1 43 0.001 Equilibrium Comp. #2 55.3 0.943.4 0.5 −1.3 Initial Comp. #3 53 5 42 0.001 Equilibrium Comp. #3 49.84.4 43.7 2.2 −6.0 Initial Comp. #4 51 10 39 0.001 Equilibrium Comp. #445.0 8.8 42.1 4.1 −11.7 Initial Comp. #5 48.5 15 36.5 0.001 EquilibriumComp. #5 40.1 13.3 40.9 5.7 −17.2

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing ethanol, comprising: hydrogenatingan acetic acid and ethyl acetate stream in a reactor in the presence ofa catalyst to form a crude ethanol product; separating at least aportion of the crude ethanol product in a first distillation column toyield a first residue comprising acetic acid and a first distillatecomprising ethanol, ethyl acetate, and water; removing water from atleast a portion of the first distillate to yield an ethanol mixturestream comprising less than 10 wt.% water; separating a portion of theethanol mixture stream in a second distillation column to yield a secondresidue comprising ethanol and a second distillate comprising ethylacetate; and hydrolyzing at least a portion of the second distillate toform a hydrolyzed stream.
 2. The process of claim 1, further separatingat least a portion of the second residue in a third column into a thirddistillate comprising ethanol and a third residue comprising water. 3.The process of claim 2, further comprising separating, prior to thehydrolyzing step, at least a portion of the second distillate in afourth column into a fourth distillate comprising acetaldehyde and afourth residue comprising ethyl acetate; and at least a portion of thefourth residue is hydrolyzed.
 4. The process of claim 1, wherein thestep of hydrolyzing is conducted under liquid phase conditions.
 5. Theprocess of claim 1, wherein at least a portion of the hydrolyzed streamis directly or indirectly returned to the reactor.
 6. The process ofclaim 1, wherein the hydrolyzed stream comprises acetic acid andethanol.
 7. The process of claim 1, wherein the at least a portion ofthe second distillate is hydrolyzed in the presence of a strongly acidicheterogeneous or homogenous catalyst.
 8. The process of claim 1, whereinthe at least a portion of the second distillate is hydrolyzed in an ionexchange reactor bed.
 9. The process of claim 8, wherein the ionexchange reactor bed is located externally from the first column andsecond column.
 10. A process for purifying a crude ethanol product,comprising the steps: hydrogenating an acetic acid and ethyl acetatestream in a reactor in the presence of a catalyst to form a crudeethanol product; separating a portion of the crude ethanol product in afirst distillation column to yield a first distillate comprising ethylacetate and acetaldehyde, and a first residue comprising ethanol, ethylacetate, acetic acid and water; separating a portion of the firstresidue in a second distillation column to yield a second residuecomprising acetic acid and water and a second distillate comprisingethanol and ethyl acetate; removing water from at least a portion of thesecond distillate to yield an ethanol mixture stream; separating aportion of the ethanol mixture stream in a third distillation column toyield a third residue comprising ethanol and a third distillatecomprising ethyl acetate; and hydrolyzing at least a portion of thefirst distillate or third distillate to form a hydrolyzed stream. 11.The process of claim 10, wherein the step of hydrolyzing is conductedunder liquid phase conditions.
 12. The process of claim 10, wherein theat least a portion of the first distillate is hydrolyzed to form thehydrolyzed stream.
 13. The process of claim 10, wherein the at least aportion of the third distillate is hydrolyzed to form the hydrolyzedstream.
 14. The process of claim 13, wherein at least a portion of thehydrolyzed stream is directly or indirectly fed to the first column. 15.The process of claim 10, wherein a portion of the first distillate and aportion of the third distillate are hydrolyzed to form the hydrolyzedstream.
 16. The process of claim 10, wherein at least a portion of thehydrolyzed stream is directly or indirectly returned to the reactor. 17.The process of claim 10, wherein the hydrolyzed stream comprises aceticacid and ethanol.
 18. The process of claim 10, wherein the at least aportion of one of the first distillate, or the third distillate, that ishydrolyzed has a molar ratio of water to ethyl acetate of at least 1:10.19. The process of claim 10, wherein the at least a portion of one ofthe first distillate or the third distillate is hydrolyzed in thepresence of a strongly acidic heterogeneous or homogenous catalyst. 20.The process of claim 10, wherein the at least a portion of one of thefirst distillate or the third distillate is hydrolyzed in an ionexchange reactor bed.
 21. The process of claim 20, wherein the ionexchange reactor bed is located externally from the first column, secondcolumn and third column.
 22. The process of claim 20, wherein at least aportion of the third distillate is fed to the ion exchange reactor bed.23. The process of claim 10, wherein the first column comprises ahydrolyzing section.
 24. The process of claim 10, wherein the firstcolumn comprises an internal ion exchange reactor bed resin.
 25. Theprocess of claim 10, wherein the first column is a reactive distillationcolumn.
 26. The process of claim 10, wherein the first column comprisesa strongly acidic heterogeneous or homogenous catalyst.
 27. The processof claim 10, wherein the hydrolzyed steam comprises at least 2% lessethyl acetate than the at least a portion of the first distillate, thethird distillate, or mixtures thereof prior to being hydrolyzed.
 28. Theprocess of claim 10, wherein the hydrolzyed steam comprises at least 10%less ethyl acetate than the at least a portion of the first distillate,the third distillate, or mixtures thereof prior to being hydrolyzed. 29.The process of claim 10, wherein the hydrolzyed steam comprises at least0.5% more ethanol than the at least a portion of the first distillate,the third distillate, or mixtures thereof prior to being hydrolyzed. 30.A process for purifying a crude ethanol product, comprising the steps:hydrogenating an acetic acid and ethyl acetate stream in a reactor inthe presence of a catalyst to form a crude ethanol product; separating aportion of the crude ethanol product in a first distillation column toyield a first distillate comprising ethyl acetate, and a first residuecomprising ethanol, ethyl acetate, acetic acid and water, wherein theweight ratio of water in the residue to water in the distillate isgreater than 2:1; hydrolyzing at least a portion of the first distillateto form a hydrolyzed stream; and recovering ethanol from the firstresidue.